Sleeping in strange places is something of a national sport in China, as demonstrated by this lorry driver, pictured next to a busy road in the city of Ningbo in 40C (104F) heat.

Image copyrightBernd Hagemann

Bernd Hagemann, who took these pictures and is the author of Sleeping Chinese, puts the nation's habit of sleeping in unconventional places down to long working hours and cramped living conditions.

Image copyrightBernd Hagemann

But he also thinks it is socially more acceptable to sleep in public in China than some other countries.

"Sleeping has - according to Chinese people - a very high rank in the list of values," he adds.

Image copyrightBernd Hagemann

Dozing in odd places is not unique to China of course, as demonstrated by this labourer in Jakarta, Indonesia, pictured lying on a pile of rice sacks.

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Michael Oko, a specialist in sleep apnoea at the Sleeping Disorders Centre, says there is no cheating the "sleep deficit". "Power naps help," he says "but they are just a temporary fix. You need sleep hygiene with a regular routine and to get between six to eight hours sleep a day. Below that, you are not going to be well."

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In the case of the Alaska Airlines baggage handler, Mr Oko says an investigation would most likely look at his recent shift patterns and whether he has any underlying sleep problems such as snoring or breath-holding.

He says men, people over 50 and those with a body mass index of more than 35 are most likely to have sleep disorders.

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"Micro sleeps" when someone sleeps for moments while doing something like driving, are the most dangerous types of naps, says Mr Oko. These Indian rickshaw pullers and taxi motorcyclists in Nigeria are luckily not at the wheel.

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In California, the competitive world of hog contests has provided for some unusual pillows.

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In space, you can slumber pretty much anywhere, as long as you don't float around and bump into things.

According to Guinness World Records, Soviet cosmonaut Gherman Titov was the first person to sleep in space.

On board the Vostok 2 in 1961 he found his arms floating in front of him, but once he secured them with a belt he claimed to have "slept like a baby".